Phenylene ether oligomers have demonstrated utility in thermoset compositions for electronics fabrication. The thermoset compositions benefit from the oligomers' high glass transition temperature, high toughness, low dielectric properties, and low water absorption. Particular advantages have been observed for bifunctional oligomers comprising, on average, about two hydroxyl groups per molecule. Such bifunctional oligomers can be prepared by copolymerizing a monohydric phenol, such as 2,6-dimethylphenol, with a dihydric phenol, such as 2,2-bis(4-hydroxy-3,5-dimethyl)propane. See, e.g., U.S. Pat. No. 7,655,278 B2 to Braidwood et al. However, use of the dihydric phenol adds substantially to cost, and there is a desire for bifunctional phenylene ether oligomers that can be readily prepared at lower cost and lower molecular weight.
Bifunctional poly(phenylene ether)s have also been prepared by reaction of a poly(phenylene ether), such as poly(2,6-dimethyl-1,4-phenylene ether), with a diphenoquinone, such as 3,3′,5,5′-tetramethyldiphenoquinone. See, e.g., U.S. Pat. No. 4,140,675 to White. However, in practice such methods have not been amenable to producing low molecular weight oligomers.
There remains a need for a process of forming bifunctional phenylene ether oligomers using diphenoquinone generated primarily or entirely in situ, rather than using a dihydric phenol.